1. Field of the Invention
This invention relates generally to an adsorbent coated biologically active biomass support for use in biological processes for the purification of waste streams, as for example industrial and municipal waste waters and to products, apparatuses and processes for use of such media. More particularly, the present invention relates to such support media which comprises a rigid or semi-rigid substrate that has an adsorbent material, capable of adsorbing pollutants and promoting their subsequent biodegradation by attached and immobilized microorganisms, bonded to the substrate, and to a bioreactor comprising the aforesaid biologically active biomass.
2. Prior Art
One of the hallmarks of contemporary civilization is that each increment of technological progress almost invariably is accompanied by a similar increment of environmental regress. As the pace of technological advances quickens, so does the march of environmental deterioration. The realization of environmental damage has occurred only relatively recently, so that present society sometimes finds itself burdened with the accumulated sins of the not-too-distant past. But another hallmark of current society is its acceptance of the undesirability of environmental degradation coupled with a determination to minimize and even reverse it wherever possible. Although the return of ground waters to their pristine condition of an earlier era is not a realistic goal, there is a genuine determination to make our waters as pure as possible. Environmental agencies have set limits for many common industrial pollutants, and as methods of pollution reduction have become more successful in reducing or removing pollutants from waste water, environmental regulations have become more stringent, resulting in an ever tightening spiral whose goal is to reduce pollutants in waste water to that minimum which is technologically feasible.
Among the methods employed to reduce or remove pollutants, bioremediation constitutes an effective and highly desirable approach. Quite broadly in bioremediation pollutants serve as a food source, generally as a source of carbon and/or nitrogen, for microorganisms. Bacterial metabolism converts the pollutants to metabolites generally with a simple chemical structure, sometimes degrading the pollutants completely to carbon dioxide and water in an aerobic process, or to methane in an anaerobic process. But in any event, the metabolites usually have no adverse environmental effects.
Various bioremediation processes are known. For example, U.S. Pat. No. 4,634,672 describes biologically active compositions for purifying waste water and air which comprises a polyurethane hydrogel containing (i) surface active coal having a specific surface according to BET of above 50 m2/g, a polymer having cationic groups and cells which have enzymatic activity and are capable of growth. U.S. Pat. No. 4,681,852 describes a process for biological purification of waste water and/or air by contacting the water or air with the biologically active composition of U.S. Pat. No. 4,634,672. The experimental examples of these patents indicate that the process is not effective for reducing contaminant concentrations in the effluent strain to less than 44 parts per million (ppm). This is not acceptable since the Environmental Protection Agency (EPA) in some instances has mandated that concentration for some contaminants (such as phenol) in effluent waste streams must be as low as 20 parts-per-billion (ppb). (See Environmental Protection Agency 40 CFR Parts 414 and 416. Organic Chemicals and Plastics and Synthetic Fibers Category Effluent Limitations, Guidelines Retreatment Standards, and new Source Performance Standards, Federal Register, Volume 52, No. 214, Thursday, Nov. 5. 1987 Public and Regulations 42522.)
Both U.S. Pat. Nos. 3,904,518 and 4,069,148 describe the addition of activated carbon or Fuller""s earth to a suspension of biologically active solids (activated sludge) in waste water as an aid in phenol removal. The adsorbent presumably acts by preventing pollutants toxic to the bacteria from interfering with bacterial metabolic activity. The patentees"" approach has matured into the so-called PACT process which has gained commercial acceptance despite its requisites of a long residence time, copious sludge formation with attendant sludge disposal problems, and the need to regenerate and replace spent carbon.
Rehm and coworkers have further refined the use of activated carbon in the aerobic oxidation of phenolic materials by using microorganisms immobilized on granular carbon as a porous biomass support system. Utilizing the propensity of microorganisms to grow on and remain attached to a surface, Rehm used a granular activated carbon support of high surface area (1300 m2/g) to which cells were attached within the macropores of the support and on its surface, as a porous biomass support system in a loop reactor for phenol removal. H. M. Ehrhardt and H. J. Rehm, Appl. Microbiol. Biotechnol., 21, 32-6 (1985). The resulting xe2x80x9cimmobilizedxe2x80x9d cells exhibited phenol tolerance up to a level in the feed of about 15 g/L, whereas free cells showed a tolerance not more than 1.5 g/L. It was postulated that the activated carbon operated like a xe2x80x9cbuffer and depotxe2x80x9d in protecting the immobilized microorganisms by adsorbing toxic phenol concentrations and setting low quantities of the adsorbed phenol free for gradual biodegradation. This work was somewhat refined using a mixed culture immobilized on activated carbon [A. Morsen and H. J. Rehm, Appl.
Microbiol. Biotechnol., 26, 283-8 (1987)] where the investigators noted that a considerable amount of microorganisms had xe2x80x9cgrown outxe2x80x9d into the aqueous medium, i.e., there was substantial sludge formation in their system.
Suidan and coworkers have done considerable research on the analogous anaerobic degradation of phenol using a packed bed of microorganisms attached to granular carbon [Y. T. Wang, M. T. Suidan and B. E. Rittman, Journal Water Pollut. Control Fed., 58 227-33 (1986)]. For example, using granular activated carbon of 16xc3x9720 mesh as a support medium for microorganisms in an expanded bed configuration, and with feed containing from 358-1432 mg phenol/L, effluent phenol levels of about 0.06 mg/L (60 ppb) were obtained at a hydraulic residence time (HRT) of about 24 hours. Somewhat later, a beri-saddle-packed bed and expanded bed granular activated carbon anaerobic reactor in series were used to show a high conversion of COD to methane, virtually all of which occurred in the expanded bed reactor; P. Fox, M. T. Suidan, and J. T. Pfeffer, ibid., 60, 86-92 (1988). The refractory nature of ortho- and meta-cresols toward degradation also was noted.
The impregnation of flexible polymeric foams with activated carbon is known to increase the ability of fabrics and garments to resist the passage of noxious chemicals and gases see for example, U.S. Pat. Nos. 4,045,609 and 4,046,939. However, these patents do not teach the use of these foams in waste water treatment, or that these foams are a superior immobilization support for the growth and activity of microorganisms.
Givens and Sack, 42nd Purdue University Industrial Waste Conference Proceedings, pp. 93-102 (1987), performed an extensive evaluation of a carbon impregnated polyurethane foam as a microbial support system for the aerobic removal of pollutants, including phenol. Porous polyurethane foam internally impregnated with activated carbon and having microorganisms attached externally was used in an activated sludge reactor, analogous to the Captor and Linpor processes which differ only in the absence of foam-entrapped carbon. The process was attended by substantial sludge formation and without any beneficial effect of carbon.
The Captor process itself utilizes porous polyurethane foam pads to provide a large external surface for microbial growth in an aeration tank for biological waste water treatment. The work described above is the Captor process modified by the presence of carbon entrapped within the foam. A two-year pilot plant evaluation of the Captor process itself showed substantial sludge formation with significantly lower microbial density than had been claimed. J. A. Heidman, R. C. Brenner and H. J. Shah, J. of Environmental Engineering, 114, 1077-96 (1988). A point to be noted, as will be revisited below, is that the Captor process is essentially an aerated sludge reactor where the pads are retained in an aeration tank by screens in the effluent line. Excess sludge needs to be continually removed by removing a portion of the pads via a conveyor and passing the pads through pressure rollers to squeeze out the solids.
H. Bettmann and H. J. Rehm, Appl. Microbial. Biotechnol., 22, 389-393 (1985) have employed a fluidized bed bioreactor for the successful continuous aerobic degradation of phenol at a hydraulic residence time of about 15 hours using Pseudomonas putida entrapped in a polyacrylamide-hydrazide gel. The use of microorganisms entrapped within polyurethane foams in aerobic oxidation of phenol in shake flasks also has been reported; A. M. Anselmo et al., Biotechnology B.L., 7, 889-894 (1985). The latter appears to be the sole report of micro-organisms entrapped within a foam used for biodegration of organic pollutants.
Known bioremediation processes suffer from a number of inherent advantages. For example, a major result of increased use of such processes is an ever increasing quantity of sludge, which presents a serious disposal problem because of increasingly restrictive policies on dumping or spreading untreated sludge on land and at sea. G. Michael Alsop and Richard A. Conroy, xe2x80x9cImproved Thermal Sludge Conditioning by Treatment With Acids and Basesxe2x80x9d, Journal WPCF, Vol. 54, No. 2 (1982), T. Calcutt and R.
Frost, xe2x80x9cSludge Processingxe2x80x94Chances for Tomorrowxe2x80x9d, Journal of the Institute of Water Pollution Control, Vol. 86, No. 2 (1987) and xe2x80x9cThe Municipal Waste Landfill Crisis and A Response of New Technologyxe2x80x9d, Prepared by United States Building Corporation, P.O. Box 49704, Los Angles, Calif. 90049 (Nov. 22, 1988). The cost of sludge disposal today may be several fold greater than the sum of other operating costs of waste water treatment.
Use of anaerobic sewage treatment systems has been offered as a solution to the sludge problem. William J. Jewel xe2x80x9cAnaerobic Sewage Treatmentxe2x80x9d, Environ. Sci. Technol., Vol. 21, No. 1 (1987). The largest difference between aerobic and anaerobic systems is in cellular yield. More than half of the substrate removal by aerobic systems can yield new microbial mass or sludge, the yield under anaerobic conditions is usually less that 15% of the organic substances removed. However, anaerobic systems are limited in the number of substrate that they can degrade or metabolize, and are not able to degrade or metabolize polynuclear aromatic hydrocarbons and non-substituted aromatic hydrocarbons such as benzene, anthracene and phenanthrene which are often present along with phenol in industrial waste waters such as coal tar processing waste waters and coke processing waste waters (See Battersby, N. S. and Wilson, Valerie, xe2x80x9cSurvey of the Anaerobic Biodegradation Potential of Organic Chemicals in digesting Sludgexe2x80x9d, Applied and Environmental Microbiology, Vol. 55, No. 2, pp. 433-439 (February, 1989). And J. M. Thomas, M. D. Lee, M. J. Scott and C. H. Ward xe2x80x9cMicrobial Ecology of the Subsurface at an Abandoned Cresote Waste Sitexe2x80x9d, Journal of Industrial Microbiology Volume 4, pp 109-120 (1989).
Another disadvantage inherent in some known bioremediation processes is that these processes do not reduce the levels of organic pollutants to reasonable levels preferable less than about 0.1 parts per million (ppm) at reasonable residence times (preferably less than about 24 hours). For example, in the process of U.S. Pat. Nos. 4,681,851 and 4,634,672 (See the specific examples), the concentration of phenol contaminants was not reduced below about 44 ppm. Thus, these processes are generally not effective for reduction of phenol to levels mandated by the EPA. (See Federal Register, Vol. 52, No. 214, pp. 42572 Nov. 5, 1987.)
This invention relates to a novel process for the purification of a wastestream, bioreactors for carrying out the purification process and novel support media for use therein.
The invention is directed to a process for purification of a wastestream comprising a pollutant which comprises: passing an aqueous influent stream, having a pollutant present at a first concentration(cl), through a bioreactor in the presence of a gas comprising an effective amount of oxygen, said bioreactor comprising a biologically active biomass which comprises a plurality of biologically active support materials, each of said support materials comprising substrate having an effective amount of an effective adsorbent for said pollutant on said substrate and having an effective amount of aerobic microorganisms capable of metabolizing said pollutant on said substrate, said adsorbent or a combination thereof, to provide an effluent stream in which the concentration said pollutant is less than cl;
wherein when the concentration of said pollutant in said influent stream is increased from c1 to a second concentration (c2) for a period of 1 hydraulic residence time (HRT), causing an increase in the concentration of pollutant in the effluent stream, the concentration of said pollutant in the effluent stream is less than or equal to about 0.15 C2 within about {fraction (1/24)} HRT or less after the end of said 1 HRT; and
wherein upon decreasing the concentration of said pollutant in said influent to C1 and maintaining the concentration of pollutant at cl for at least 1 HRT, the concentration of the pollutant in the effluent stream decreases to less than or equal to about 0.12 C1 within about 1 HRT or less.
Several advantages flow from the novel process of this invention. An important benefit which flows from this invention is that our process is resistant to upset.
Resistant to upset describes the ability of the process to reduce efficiently the contaminant level of waste streams having a relatively high level of contaminants to a desired level, preventing intermittent contaminant levels in the effluent above a desired level. For example, in certain preferred embodiments of this invention, concentration levels of organic pollutants in the feed stream can be as high as about 5000 parts-per million (ppm) which through use of the process of this invention can be reduced to levels as low as 1 ppm, or 0.1 ppm or for that matter 20 parts-per-billion (ppb). This advantage is of immediate and substantial economic benefit in that it obviates the need for time consuming and expensive pretreatment processes for reducing the amount of contaminant in the aqueous stream directly exiting the manufacturing process before introducing the stream into a bioremediation process. Our process provides for continuous treatment of a waste stream such that the concentration of pollutant in the effluent stream is maintained below EPA mandated levels. In addition, since our process can remediate relatively high levels of pollutants, the likelihood of a pollutant-cotaining waste stream deactivating the microorganisms killing or hindering their pollutant-degrading ability is significantly reduced.
Another advantage of preferred embodiments of this invention is that the process can be used in a fixed bed reactor system to reduce relatively high levels of organic pollutants in aqueous feed streams to relatively low levels with the additional benefit of significantly less sludge formation than that from currently available systems, affording important advantages in sludge disposal costs.
Another unique advantage of this invention is that significant reductions in levels of organic contaminants contained in the effluent stream are obtained with reasonable hydraulic residence times as compared to prior art processes as for example, the process described in U.S. Pat. Nos. 4,634,672 and 4,681,851. For example, experimentation has demonstrated that in certain most preferred embodiments of the invention, the level of effluent phenol in phenol containing aqueous waste streams can be reduced to concentrations as low as 20 parts per billion at hydraulic residence times as short at 24 hours. This is also not a trivial benefit especially in view of the low levels of various organic pollutants such as phenol in aqueous waste streams from industrial processes set by the Environmental Protection Agency and the economic requirement that these reduced levels be obtained over reasonable time periods.
A As measured by its performance characteristic relative to prior art processes, the process of this invention is a marked improvement over the prior art and relative to the prior art represents a difference in kind rather than a difference in degree.